This application is related to applicant's copending U.S. patent application Ser. No. 08/177,840 entitled FLYWHEEL-DRIVEN FASTENER DRIVING TOOL AND DRIVE UNIT filed on even date herewith and naming as inventors J. Crutcher, D. Lucas, D. D'Amico and E. Hunter.
This invention relates to an apparatus for controlling electric motors. While the invention has many varied applications, it will, for the purpose of clarity, be described herein as used to control a motor mounted to drive the flywheel of a fastener applying tool. This description is by way of example only, and it will be appreciated that the invention has many varied uses and applications in motor control.
In the past, where relatively large energy impulses are needed to operate a fastener driving tool (such as a nailer or stapler) for framing purposes, for example, it has been common to power such tools pneumatically. Pneumatic fastener driving tools, which require a job site compressor, are well known. Such tools are capable of driving a nail or staple of 3" or longer into a framing wood, such as 2.times.4s, for example.
Electrically driven tools, such as solenoid operated fastener driving tools, are also well known. These are primarily used in lighter duty applications such as in driving one inch brad nails, for example, rather than the larger 2" to 4" staples or nails used in framing.
Considerable thought and effort has been expended in providing a heavy duty, i.e. high powered, fastener driving tools without relying on a compressor. One alternative approach is employing flywheels as a means to deliver kinetic energy sufficient to power a heavy duty fastener driver. Examples of such systems are disclosed in U.S. Pat. Nos. 4,042,036; 4,121,745; 4,204,622 and 4,298,072 and in British Patent No. 2,000,716.
While a great deal of time has been expended in the development of flywheel driven fastener driving tools, nevertheless, such tools still present their own unique problems. For example, in tools utilizing two flywheels, it has been the practice to provide a separate electric motor for each flywheel. The two motors add considerable weight and bulk to the tool and are difficult to synchronize. Another approach is to mount one of the flywheels on the electric motor shaft and then drive the second flywheel through a series of belts or chains and pulleys. Such drives are complex, difficult to adjust and are subject to wear.
Another problem area in such tools involves the apparatus to cause one of the flywheels to move toward and away from the other. Preferably, for example, a movable flywheel is shifted into an operative position with an adjacent flywheel wherein its periphery is spaced from the periphery of the stationary flywheel by a distance less than the nominal thickness of the thick part of the driver, so to punch and thrust the driver between the two wheels. The movable flywheel is then shifted in the opposite direction to an inoperative position wherein its periphery is spaced from that of the fixed flywheel by a distance greater than the greatest nominal thickness of the driver, so the drive can be returned for another stroke. Heretofore, systems to bring about this shifting of one of the flywheels with respect to the other have been cumbersome, complex and not altogether satisfactory.
Yet another area of concern in these tools is directed to the means for returning the driver to its normal, retracted position from the end of the drive stroke. Complex systems of springs, pulleys and elastomeric cords have been developed. Such systems, however, have proven to be subject to wear, stretching and deterioration due to stresses and to lubricants and foreign materials within the tool housing. Where a spring is used, the extent of its stroke or travel has been too great, and the spring fails early, requiring replacement. Other systems have employed a powered return roller and an idler roller which shifts a free floating driver to its normal position after the drive stroke. These systems were also found to be less than satisfactory.
In addition to these concerns, the nature in which such tools are used presents additional problems when the use of flywheels, as energy devices, is considered. Specifically, when a flywheel-powered tool is fired or cycled, energy is transferred from the flywheel to the fastener driver or ram, for example, for driving a fastener. In essence, the flywheel is rotated at a speed which provides sufficient rotational inertia such that, when coupled to the fastener driver, there is sufficient power to drive a long framing fastener into a target. For example, a typical framing fastener is about 31/2" to 4" long and may require up to 50 horsepower to drive it full length into wood.
When a flywheel is used to drive a fastener, the energy used is apparent in a reduction of the desired initial or starting flywheel speed. That desired or initial speed must be regained before a fastener driving operation at the same power can be repeated. The time intervals, however, needed to accelerate the flywheel back up to the desired or set speed may lag far behind the frequency with which the user desires to set another fastener. In other words, physical limitations of the known flywheel energy systems in such tools limit the frequency or repetition rate with which they can be used.
While a flywheel energy system might be designed to deliver several energy impulses of similar power but over increasing time increments, as the wheel winds down, such functioning as a practical matter is difficult to control. It is thus desirable to provide a flywheel-operated tool where a flywheel is accelerated very quickly to its desired or initial speed and within the time interval required by normal use frequencies.
An associated consideration is that the desired speed to which the flywheel is accelerated is repeatably and consistently regained and accurately regulated. Overshoots, undershoots or drifting of the desired speed result in overpowered or underpowered fastener driving which sets fasteners either too deeply or not deeply enough.
Another consideration in fastener driving is the variation both in length or configuration of fasteners and the variation of materials into which fasteners are driven. It is desirable that a heavy duty fastener driving tool be adjusted to accommodate such variations, yet at the same time be capable of quickly and consistently repeating a fastener driving operation within the selected range of operation.
More specifically, given the mechanical and dimensional specifications of the flywheel and knowing the driving forces which must be applied by the tool, the range of required angular speeds of the flywheel can be determined. In order to achieve the necessary consistency and repeatability of the driving action without overdriving or underdriving the fastener, the speed of the electric motor connected to the flywheel must be regulated within .+-.1%. A typical selectable range of angular velocities of the motor required by the range of driving forces, is from 7,000 revolutions per minute (rpm) to 15,000 rpm, when used with flywheels, for example, weighing 0.87 pounds and having a movement of inertia of 4.016.times.10.sup.-4 ft. -lbs.sec.sup.2. Further, when the tool drives a fastener, the kinetic energy is expended and the speed of the flywheel is reduced. The motor must be accelerated back to the selected speed within 500 milliseconds. It is also necessary that the motor and its control be immune from a high noise environment, for example, both radiant and power line noise may be created by other high power equipment and brush noise within the motor itself. In addition, the driving tool is often used in environments of temporary power hook ups in which significant voltage fluctuations are frequent and severe. The motor and its control must have minimum weight and cost in order to be commercially viable in a portable hand-held tool.
It is known that there are currently many motor speed controls for different types of motors. For example, a Motorola TDA 1085C is an integrated circuit component providing a universal motor speed control which uses triac phase angle control with a voltage comparison velocity feedback loop. There are many references to motor speed controls utilizing phase locked loops primarily for the control of brushless DC motors. The theory and feasibility of using a phase locked loop in the control of universal AC/DC motors in lieu of phase angle control is also known. Further, there are existing portable hand held tools in which speeds are selectable. However, those systems typically are open loop in nature and do not require a precise closed loop speed control. Such open loop speed control systems may be obtained by switching power to the motor between a half wave and a full wave power supply or switching selected motor coils into and out of the circuit or by mechanical gearing. Further, portable hand held tools which are battery powered typically pulse width modulate current to a permanent magnet field coil motor.
None of such known circuits are capable of providing a speed control for a universal AC/DC motor useful in a hand-held portable device with the speed range, precision and response time requirements of the present invention.
Consequently, heretofore there has not been available in the industry a reliable, lightweight and relatively simple electromechanical fastener driving tool which can efficiently, consistently and repeatably drive fasteners of various sizes, and particularly those sizes needed in heavy duty framing applications.
A further consideration with electric tools, particularly with flywheel-operated or other hand tools, is the weight and expense of the drive unit. Motors with sophisticated speed controls can be very heavy and expensive. It is thus desirable to provide fastener driving tools or drive units for tools, implements or other devices with relatively lightweight, speed controlled motors at a relatively low cost.
With hand-held or hand-operated tools, it is desirable not only to provide a relatively lightweight energy source, but to provide a tool or implement which is balanced. In the prior application identified above, a fastener driving tool is powered by a flywheel driven by a motor, where both flywheel and motor are located in the forward end of the tool. The center of gravity of such a device is forward, and it is difficult to balance the tool. On the Other hand, moving the motor away from the flywheel requires a coupling or extended drive which increases tool weight, and drains effective power. This may require a larger motor with the attendant weight increases. It is thus desirable to provide an improved, well-balanced hand-held fastener driving tool, and a drive unit facilitating the balance of such hand-held tools.
While the noted considerations are important to fastener tools and their particular application, the operation of many tools, implements and devices requires the application of a motive force or energy pulse to a working member. Many such apparatus require only a short or limited motion of such an implement or member to accomplish a task. Currently, in addition to the flywheel and pneumatic systems noted above, such apparatus are powered electrically, or hydraulically, by motors or solenoids, for example, by internal combustion devices, springs or other devices. By way of example only, devices other than fastener driving tools which require or utilize various energy sources to move a working member include: paper punches, diverse material punchers, shears, cutters, pruners, wrenches, stitchers, riveters, pulverizers, tampers, aerators, slippers, chisels, material handling devices, hammers, hammer drills, embossers, pumps, coining devices, clamps, and tools or implements for many other applications. It is desirable to provide an improved drive or power unit for such tools.
One object of the invention is to provide a low cost, reliable and light weight motor control which provides accurate speed control for a motor.
A further objective of the invention is to provide a motor control having a wide range of motor speeds selectable by an operator and the capability of automatically and rapidly accelerating back to a selected speed after a loss of speed caused by the imposition of a load on the motor.
A further objective of the invention to provide an improved apparatus for delivery of an energy pulse to a working member.
A further objective of the invention has been to provide an improved apparatus for delivering an energy pulse from a flywheel to a fastener driver or to the working member of a tool or implement.
A further objective of the invention has been to provide a motive apparatus and a control therefor for driving a flywheel at a selected speed, and for regaining that speed quickly after a speed reduction.
A further objective of the invention has been to provide an improved flywheel-driven fastener driver capable of producing desired energy pulses at desired cycle frequencies.
A further objective of the invention has been to provide an improved portable hand-held power tool.
To these ends, one preferred embodiment of the invention comprises a power or drive unit in operative disposition in a fastener driving tool. A flywheel is mounted in a tool housing and a handle extends rearwardly from the housing with a motor for driving the flywheel being mounted at a distal end of the housing. A drive shaft coupled to the motor has a pinion with spiral bevel gear teeth meshing with similar teeth on the flywheel. The motor weight at the handle's rear end tends to balance out the tool housing and its components so the entire tool feels balanced.
A drum is mounted in the housing. It includes a first circumferential surface. A first drive cable is secured to the drum so as to be wound up on the surface when the drum rotates. A cone clutch is utilized to selectively and intermittently interconnect the flywheel to the drum to impart a pulse of energy to the drum to rotate it and wind up the cable onto the drum. The other end of the cable is attached to a fastener driver. When the drum is rotated, the cable is wrapped onto the drum, and pulls the driver to engage and drive a fastener. The energy stored in the flywheel is thus delivered to the fastener through the drum, cable and fastener driver.
Another or a second circumferential surface, having a diameter preferably smaller than the first circumferential surface, is operatively secured to the drum. A second, or return, cable is attached to the second surface and is wound thereabout when the drum is rotated by the flywheel. The other end of the second return cable is attached to a coil spring which is compressed when the return cable is wound up. After the clutch disengages the drum from the flywheel, this spring expands to tension the second return cable, reversing the drum and pushing the first cable and fastener driver back to a start position. Since the return cable wind-up surface is of less diameter than the drive cable surface, the second return cable does not traverse so much distance as the drive cable when the drum is actuated by the flywheel and clutch. The spring travel is thus held within a range which does not unduly stress or fatigue the spring despite extensive cycling of the tool.
Trigger actuated linkage and an axially expansible actuator serve to actuate the clutch to momentarily interconnect the flywheel to the drum. The actuator is similar in structure and operation to the prior application incorporated by reference herein.
An relatively simple and inexpensive AC/DC motor is used. A control operates the motor at a selected speed depending on fastener length and configuration and on target parameters. The control serves to accelerate the motor, and the flywheel back to an initial speed with only a very short delay of about 500 milliseconds; well within the period of the desired frequency of use.
The speed of the universal AC/DC motor is controlled by switching the phase angle of an AC signal with a triac power switch in response to a motor control providing phase-locked loop velocity control. The triac power switch is connected between the source of AC power and the motor and has a trigger input for controlling the application of the AC signal to the motor. An analog reference circuit is responsive to the AC signal and initiates a ramp signal with each zero crossing of the AC signal. The ramp signal has a duration approximately equal to the duration between zero crossings of the AC signal.
A speed command circuit provides a speed command signal having a reference frequency representing one of several selectable desired speeds of the motor. A feedback circuit is responsive to rotation of the motor and produces a feedback signal having a feedback frequency representing the actual speed of the motor. A phase detector produces an error signal representing the phase difference between the speed command and the feedback signals which is averaged by a low pass filter. A comparator produces a trigger pulse to the triac power switch during each occurrence of the ramp signal as a function of the detected phase difference, The leading edge of the trigger pulse occurs at a time during the ramp signal that is determined by the phase difference between the reference and feedback frequencies. The trigger pulse switches the triac as a function of that phase difference, and the AC signal is applied to the motor to lock the phase of the speed command and feedback signals thereby maintaining the actual motor speed equal to the desired motor speed.
A fastener driving tool embodying the invention may also include a fastener magazine which is not only inclined, but curved, and which extends rearwardly toward the motor on the handle's rear end, from a forward position below the driver, partially encircling the handle, and helping balance the tool.
The power or drive unit such as described can be used with various tools, implements or other devices to impart a pulse of energy to a movable or working member thereof. Such a unit includes the motor, motor control driveshaft, flywheel, drum, drive and return cables, clutch trigger linkage, and clutch actuator. Where the balance and/or portability is of no concern, the motor may be mounted to directly drive the flywheel. A hand tool embodying the invention may also include a tool housing, a handle extending therefrom, a motor in a distal end of the handle and a shaft through the handle coupling the motor to a flywheel in the housing, together with a control for accelerating the motor and flywheel to predetermined speeds in a minimum time period.
The present invention has the advantage of providing very accurate speed control of the motor and a very fast response to speed deviations from a selected speed. A further advantage is realized because the frequencies of the speed command and feedback signals are less susceptible to noise. A further advantage is that the above features are provided by a low cost, light weight and reliable motor control.